There is known a buckle device which includes a tongue plate slidably provided along a longitudinal direction of a webbing and a buckle main body engaged with the tongue plate. The buckle main body includes a release button and a cover accommodating the release button. A part of the cover forms a tongue plate guide portion, and a tongue plate insertion port is formed between the tongue plate guide portion and the release button.
Further, a frame for slidably supporting the release button is disposed in the cover. The frame has a bottom wall forming a wall surface continuous with the tongue plate guide portion of the cover, and a pair of side walls standing from both end portions of the bottom wall. The frame has a U-shaped cross section.
Generally, a guide portion for guiding a tongue plate inserted from a tongue plate insertion port is provided in the vicinity of the tongue plate insertion port on a pair of side walls of a frame. However, when the tongue plate is inserted into the tongue plate insertion port in a state of being obliquely inclined, the tongue plate may get caught in the guide portion. In order to solve this problem, a buckle device 100 disclosed in JP-B-3886087 and shown in FIG. 8 is configured in such a manner that a release button (described as an operation button in JP-B-3886087) 110 is provided with a side wall 111 located inside of a guide portion 121 of a frame 120 and protruding downward from the guide portion 121.
However, in the configuration as shown in FIG. 8, the release button 110 is made of a resin. Therefore, when a tongue plate 130 is inserted into a tongue plate insertion port with a relatively large force in a state of being obliquely inclined, the side wall 111 may be bent and the tongue plate 130 may collide with the guide portion 121. The frame 120 including the guide portion 121 and an insertion portion (the portion inserted into the tongue plate insertion port) of the tongue plate 130 are made of a metal. Therefore, when the tongue plate 130 collides with the guide portion 121, there is a possibility that both are damaged.